The present invention relates to local area network systems for use with computer and office automation systems and is more particularly concerned with arrangements for defining time slots on the common communication medium which is operated on a time division multiplex basis.
A typical example of time division multiplex operated systems is shown in U.K. Pat. No. 1,314,180. In such systems there is a common medium for communication and each subscribers station connected thereto contains its own control and clocking system. Typically a crystal controlled oscillator experiences drift of the order of one in 10 which, at a transmission bit rate of the order of 5.12M bits per second, gives a one bit drift in every six frames. The system clock is arranged to divide down the bit rate oscillator to produce common medium time slots and frames for the station. The multiplexing system used in such a local area network requires to pack the time slots as closely together as the delay between the most separated subscribers stations will allow, to efficiently use the common medium.
It is an object of the present invention to achieve the above requirement.